The simplest way for this is to create your one line, then run it through an external filter. With the cursor on the same line, type

!!awk ' {for(i=0;i<100;i++) print'

If you find yourself doing this a lot, type the line into your buffer this way:

!!awk ' {for(i=0;i<100;i++) print'^V^M

i.e., append a carriage return to the line. Now go to the beginning of the line and type

"dD

Now "@d" will replace whatever line you're on with 100 copies of it.